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Zurich Open Repository andArchiveUniversity of ZurichMain LibraryStrickhofstrasse 39CH-8057 Zurichwww.zora.uzh.ch
Year: 2012
Effect of surface conditioning with airborne-particle abrasion on the tensilestrength of polymeric CAD/CAM crowns luted with self-adhesive and
conventional resin cements
Stawarczyk, Bogna ; Basler, Tobias ; Ender, Andreas ; Roos, Malgorzata ; Özcan, Mutlu ; Hämmerle,Christoph H F
Abstract: Airborne-particle abrasion before cementation of polymeric CAD/CAM crowns minimallyimproved the tensile strength. Both the failure types and the tensile strength values of adhesively lutedglass ceramic crowns showed superior results to adhesively cemented polymeric ones. Although the tensilestrength results were low, crowns cemented with RXU showed, after aging, the highest tensile strengthof all other tested groups.
DOI: https://doi.org/10.1016/S0022-3913(12)60031-6
Posted at the Zurich Open Repository and Archive, University of ZurichZORA URL: https://doi.org/10.5167/uzh-58927Journal ArticleAccepted Version
Originally published at:Stawarczyk, Bogna; Basler, Tobias; Ender, Andreas; Roos, Malgorzata; Özcan, Mutlu; Hämmerle,Christoph H F (2012). Effect of surface conditioning with airborne-particle abrasion on the tensilestrength of polymeric CAD/CAM crowns luted with self-adhesive and conventional resin cements. Jour-nal of Prosthetic Dentistry, 107(2):94-101.DOI: https://doi.org/10.1016/S0022-3913(12)60031-6
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19228
Effect of surface conditioning with air-abrasion on the tensile strength of polymeric CAD/CAM
crowns luted with self-adhesive and conventional resin cements
ABSTRACT
Statement of problem. Adhesively bonded, industrially polymerized resins have been suggested
as permanent restorative materials. It is claimed that such resins present similar mechanical
properties to glass ceramic.
Purpose. To assess the tensile strength of polymeric crowns following different conditioning
protocols; luted with self-adhesive cements to dental abutments and with conventional resin
cements.
Material and methods. Human teeth were prepared for all crowns and divided into 13 groups
(N=312, n=24 per group). Polymeric crowns were CAD/CAM fabricated, and divided into 3
groups depending on different surface conditioning methods: A) No treatment, B) airborne
particle abrasion with 50 µm alumina, and C) airborne-particle abrasion with 110 µm alumina.
Thereafter, the crowns were luted on dentin abutments with the following cements: 1) RXU
(RelyX Unicem, self-adhesive), 2) GCM (G-Cem, self-adhesive), 3) ACG (artCem GI,
conventional), and 4) VAR (Variolink II, conventional). Glass ceramic crowns milled and
cemented with dual-polymerized resin cement (Variolink II) acted as the control group. The
tensile strength was measured initially (n=12) and after aging by mechanical thermocycling
loading (1 200 000 cycles, 49 N, 5°C to 50°C) (n=12). The tensile strength (MPa) of all crowns
was determined by the pull-off test (Zwick/Roell Z010; Ulm, Germany, 1mm/min).
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Subsequently, the failure types were classified. Data were analyzed with 2-way and 1-way
ANOVA followed by a post hoc Scheffé test and t-test (α=.05).
Results. No adhesion of the tested cements was observed on unconditioned polymeric
CAD/CAM crowns and those luted with VAR. Among the tested cements, GCM showed
significantly higher values after air-abrasion with 110 µm (initial: 2.8 MPa; after aging: 1 MPa)
than 50 µm alumina (initial: 1.4 MPa; after aging: 0 MPa). No significant effect was found
between 50 and 110 µm particle size alumina in combination with the other 2 cements. After
aging, the tensile strength of the crowns luted with GCM (50 µm: 0 MPa and 110 µm: 1 MPa)
and ACG (50 µm: 1 MPa and 110 µm: 1.2 MPa) was significantly lower than those luted with
RXU (50 µm: 1.9 MPa and 110 µm: 2 MPa). All air-abraded polymeric CAD/CAM crowns
(initial: 1.4-2.8; 0-2 MPa) showed significantly lower tensile strength values than the control
group (initial: 7.3 MPa; after aging: 6.4 MPa). While with all polymeric specimens, failure type
was adhesive between the cement and the crowns, the control group showed exclusively
cohesive failures within the ceramic.
Conclusion. Air-abrasion before cementation of polymeric CAD/CAM crowns has minimally
improved the tensile strength. Both the failure types and the tensile strength values of adhesively
luted glass ceramic crowns showed superior results to adhesively cemented polymeric ones.
Although the tensile strength results were low, crowns cemented with RXU showed, after aging,
the highest tensile strength of all other tested groups.
Clinical Implication. The adhesion of tested polymeric CAD/CAM crowns to dentin was
considerably lower than that of the glass ceramic crowns.
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INTRODUCTION
Computer aided design and computer aided manufacturing (CAD/CAM) technology
allow the production of dental restorations with numerical controlled machining. This technology
has been successfully established for milling ceramic materials and other materials have recently
been introduced as an economic alternative to ceramics for dental reconstructions, with lower
expenditure of time and costs. One such example is polymeric CAD/CAM blocks for interim
dental restorations.1 Such materials are based on polymethylmethacrylate (PMMA), urethane
dimethacrylate (UDMA), and bisphenolglycidyldimethacrylate (BisGMA) types of resins.
Since these CAD/CAM blocks are industrially polymerized under high pressure and
temperature, they present superior mechanical properties to the manually polymerized resins.1-3
In general, although the manually polymerized resins show lower fracture resistance, they are
only indicated for interim fixed dental prostheses (FDPs).1-3 Because of their good optical and
mechanical properties, as well as their less abrasive effect on the antagonist enamel,4 recently
introduced polymeric CAD/CAM blocks are considered as alternative materials to glass
ceramic.5 However, limited information is available on their mechanical durability with and
without aging regimens.1,3 Alt et al1 reported that after 3 months of water storage at 37°C and
5000 thermocycles, industrially polymerized 3-unit FDPs showed significantly higher fracture
load than manually polymerized ones.
Since these materials are also indicated for long-term restorations, their adhesion is of
importance for their durability. To the authors` best knowledge, at present, there is no
information available on the retentive strength of polymeric CAD/CAM crowns. Adhesion of
resin-based cements includes both conditioning the cementation surface of the restorations as
well as the prepared dentin. One of the most common methods of conditioning polymeric
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materials is the use of airborne-particle abrasion, which in principle cleans the surface and at the
same time increases the surface area.6,7 Similar effects are observed in glass ceramics after
hydrofluoric acid etching.8
Adhesion has 2 aspects, and for durable restorations not only the conditioning of the
restorative material but also the dentin is crucial for adequate bonding of the resin cement to both
substrates. Etching-and-rinse bonding systems are considered as the gold standard for
conditioning dentin. However, because of their technique sensitivity, some of the conventional
resin cement systems have involved self-etch adhesives. These self-etch adhesive cements do not
require conditioning of the dentin, which eliminates technique sensitivity.9
The adhesion of such cements could be individually tested either on the restoration
material or on the tooth substrate.10,11 However, in order to simulate a more realistic clinical
environment , investigation of the tensile strength of luting agents can be studied by using a pull-
off test involving axial dislodgement forces acting on crowns luted to extracted human teeth.12-16
The aim of this study was to investigate the effect of air-abrasion with 2 particle sizes of
the abrasive and resin cements on the tensile strength of polymeric CAD/CAM crowns bonded to
dentin. The null hypotheses tested were that polymeric and glass-ceramic crowns conditioned or
non-conditioned would not show significant difference in terms of tensile strength.
MATERIAL AND METHODS
Extracted caries-free molars (N=312) were collected, cleansed of periodontal tissue
residues and stored in 0.5% Chloramine T at room temperature for 1 week. Thereafter, they were
stored in distilled water at 5°C for a maximum of 6 months.17 The roots of each tooth were
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embedded with acrylic resin (ScandiQuick: SCAN DIA; Hagen, Germany) in a special device
held parallel to the long axis of the tooth.
The teeth were prepared with a motorized parallelometer (PFG 100: Cendres Métaux;
Biel-Bienne, Switzerland) with a conicity of 10 degrees, and the shoulder preparation was made
with a 40 µm diamond rotary cutting instrument (FG 305L/6: Intensiv SA; Grancia,
Switzerland). To obtain a standardized coronal height of 3 mm, the holding device was
positioned in a cut-off grinding machine (Accutom-50: Struers GmbH; Ballerup, Denmark). The
coronal line angles were rounded with a polishing disc (Sof-Lex 1982C/1982M: 3M ESPE;
Seefeld, Germany). The specimens were stored in water at 37°C before cementation and testing.
The prepared abutments were scanned with a Cerec 3D camera (Sirona; Bensheim,
Germany) and the bond surface area was calculated (Cerec Software 2.80 R2400 Volume
Difference: Sirona). The crowns were designed (Cerec InLab 3D Program Version 3.10: Sirona)
for each abutment and milled with Cerec InLab XL (Sirona).
The 288 tooth specimens with milled polymeric CAD/CAM crowns were divided into 3
main pretreatment groups (n=96). Within main group 1, the polymeric crowns were not treated.
Within main group 2, the crowns were air-abraded with alumina powder with a mean particle
size of 50 µm (LEMAT NT4: Wassermann; Hamburg, Germany) for 10 s at a pressure of 0.2
MPa from a distance of 10 mm. Within main group 3, the crowns were air-abraded with alumina
powder with a mean particle size of 110 µm as described for main group 2. Subsequently, the
polymeric crowns of each main group were cemented according to the manufacturers`
instructions under 100 N load on dentin abutments with the following resin cements (n=24 per
resin cement): RelyX Unicem (RXU: 3M ESPE), G-CEM (GCM; GC Europe; Leuven,
Belgium), artCem GI (ACM: Merz Dental; Lütjenburg, Germany), and Variolink II (VAR:
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Ivoclar Vivadent) (Table I). The size of the specimen (n=12 per subgroup) was based on a
previous study, which showed significant differences with a similar specimen size.13 No formal
power analysis was performed prior to initiation of the study. The cements were occlusal
photopolymerized for 30 s (Elipar S10, 3M ESPE). Then the specimens in all groups were stored
in an incubator for 10 min at 37°C and loaded in a special device with 100 N for simulating
finger pressure during cementation of a crown.18
For the control group, conventional glass ceramic crowns (VITA Mark II: VITA
Zahnfabrik; Bad Säckingen, Germany) were etched (9% buffered hydrofluoric acid: Ultradent
Products; South Jordan, Utah) and treated with a silane coupling agent (Monobond S: Ivoclar
Vivadent; Schaan, Liechtenstein) and an adhesive (Heliobond: Ivoclar Vivadent) according to
the manufacturer’s instructions. The abutment surfaces were conditioned with Syntac Classic
(Ivoclar Vivadent), and crowns were cemented with resin cement (Variolink II: Ivoclar
Vivadent) according to the manufacturer’s instructions.
While the initial tensile strength was measured in half of each group (n=12), the other
half (n=12) was subjected to mechanical thermo-mechanical cyclic loading (chewing simulator,
University Zurich). The crowns were loaded under vertical compressive load with 49 N for 1.2
million times at 1.67 Hz frequency. Mesiobuccal cusps from nearly identical maxillary human
molars fixed in amalgam were used as antagonists and loading points. The specimens were fixed
to a holder simulating the physiologic tooth movements in the lateral direction.
Simultaneous thermocycling was achieved by changing the surrounding water
temperature in the chamber every 120 s from 5°C to 50°C. In total, the temperature changed 6
000 times during the occlusal loading.19-21 To embed the crowns in the upper holding devices and
position the lower holding devices parallel maintaining a 1.5 mm space between them, the space
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between the lower holding devices was filled with an addition silicone (Lab Putty:
Coltène/Whaledent; Altstätten, Switzerland). Acrylic resin (ScandiQuick) could be poured
through the screw hole in the bottom of the holding device.
The crowns were pulled out under tensile load (Universal Testing Machine, Zwick/Roell
Z010: Zwick; Ulm, Germany) at a cross head speed of 1mm/min until debonding of the crowns
or facture tooth/crown took place (Fig. 1). The tensile strength of specimens that crowns
separated from the debonded tooth before actual testing was considered as 0 MPa. The bond
strength values were calculated (fracture load/bond area = N/mm² = MPa).
The failure types after testing were classified into 3 main groups: 1) failure at the
interface of dentin and cement, 2) mixed failure, and 3) failure at the interface of polymeric
crown and cement. For the failure type classification, an optical microscope at a ×25
magnification was used, and digital photos were made (Tesovar: Zeiss; Zurich, Switzerland) to
collect more detailed information on the observed failure types.
The statistical analysis was made by using Statistical Package for the Social Science
Version 15 (SPSS INC, Chicago, Ill). Descriptive statistics were computed. Within each
pretreatment and aging group, the differences between the mean tensile strengths of different
cement groups were investigated by 1-way ANOVA followed by Scheffé test. Additionally,
Student’s t-test was applied to investigate the influence of pretreatment for each cement type and
aging group separately. P-values smaller than 5% were considered to be statistically significant
in all tests. Power analysis using a two group Satterthwaite t-test with a 0.05 two-side
significance level was performed with respect to the main finding of the measured tensile
strength data using nQuary 6.0 (Statistical Solution, Saugus MA, USA).
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RESULTS
The power analysis was performed for two aged groups: control group and RXU air-abraded
using 110 µm alumina (Table II). A simple size of n=12 in each group will have 99% power to
detect a difference in means of 4.4 given the observed deviations in both groups.
The nonconditioned polymeric crowns with all cement groups and those cemented after
air-abrasion with VAR fractured before the actual tensile strength measurements under both
nonaged and aged conditions. These were considered as 0 MPa (Table II, Fig. 2).
Except for the air-abraded (50 µm alumina) and aged GCM group, where all specimens
were debonded after mechanical thermocycling loading, all other air-abraded groups showed
significantly higher results than nontreated groups (Table IV).
The GCM group (initial and after aging) air-abraded with 110 µm alumina showed higher
tensile strength results than those abraded with 50 µm alumina. Within the 50 µm alumina air-
abraded groups, GCM showed the lowest initial tensile strength.
No significant differences were found with 110 µm alumina air abrasion among the
initial test groups. After aging, the tensile strength of RXU was significantly higher than that of
GCM.
All specimens fractured adhesively between the cements and the polymeric crowns (Fig.
3B).
The adhesively luted glass ceramic crowns (control group) showed the highest tensile
strength of all other test groups before and after mechanical thermocycling loading (Table II, Fig.
2). During the measurement of tensile strength, the glass ceramic crowns fractured cohesively at
all times (Fig. 3A). Aging did not significantly influence the results in the control group (Table
III).
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DISCUSSION
All tested cements showed no bonding when polymeric crowns were untreated. Pretreatment
with alumina increased the results, except for VAR. This phenomenon can be explained by the
fact that the both self-adhesive resin cements, GCM and RXU contained methacrylate monomers
with acidic groups that eventually copolymerized with the industrially polymerized CAD/CAM
resin. On the other hand, VAR is conventional resin cement based on Bis-GMA, TEGDMA,
UDMA monomers that possible did not copolymerize with the CAD/CAM resin tested. The
tensile strength of pretreated polymeric crowns cemented with all tested cements presented
significantly lower values than those of the adhesively luted glass ceramic crowns. Therefore, the
first part oft he null hypothesis of this study was rejected.
The glass ceramic crowns showed the highest tensile strength among all tested groups. In
all specimens of this group, the glass ceramic crowns fractured cohesively. Consequently, the
measured tensile strength of adhesion exceeded the cohesive strength of the ceramic itself.
Therefore, this test method could not be adapted for glass ceramic crowns because of the lower
flexural strength of the ceramic tested.5 This phenomenon has also been observed with other test
methods such as shear bond strength testing, where failure type is often cohesive in the glass
ceramic.11
In this study, the second hypothesis tested the impact of air abrasion on the tensile
strength of polymeric CAD/CAM crowns and nontreated ones. The air-abraded polymeric
crowns presented higher tensile strength at all times, except for VAR. Therefore, the second part
of the null hypothesis is also rejected. The reason for no adhesion with VAR, could be the lack of
silane application. Since the study tested only the effect of micromechanical bonding, in these
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groups, no silane was applied. The adhesive failure type between the cement and the intaglio
surfaces of all crowns showed clearly that the adhesion of these cements was higher to the dentin
than to the crowns.
Air abrasion principally cleans and increases the surface area, resulting in higher bond
strength due to mechanical retention.6,7 Based on the results of this study, the adhesion between
the polymeric crowns and the resin cements could be considered as mechanical retention. The
polymeric blocks are industrially polymerized and present a high degree of conversion than
manually polymerized ones.22 Since the nontreated group showed no bonding, it can be stated
that free radicals were not sufficient to achieve adhesion between the studied cements and the
intaglio surfaces of the crowns. In this case, the use of conventional cement such as zinc
phosphate could be an option. Regardless of the cements used, retention of the crowns is
dominated by the parallelism of the preparation and the height of the crowns after preparation.
This study used the pull-off test with prepared human teeth, where polymeric CAD/CAM
crowns were bonded according to standard clinical procedures. However, the teeth were prepared
manually, and the water supply was not controlled with the handpiece as under clinical
conditions. In a previous study, where the tensile strength of zirconia crowns cemented with self-
adhesive resin cements on dentin were tested,13 the results ranged between 7.3 MPa and 14.1
MPa. Although the identical experimental set-up was used, the results of this study indicated
inferior adhesion of 2 of the cements (RXU, GCM) on the polymeric crowns.
The advantage of using pull-off-tests is the integration of the surface bonded area into the
calculation. It can be assumed that the applied method presents a more precise calculation than
previously published studies.12,14,16,17 In 1 study, the bond area was measured by wrapping 0.1
mm tinfoil around the preparation to determine the weight of the foil.12,14 In 2 other studies16,17the
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bond area of the specimens was calculated by using the formula for a truncated cone, to which
the area of the flat occlusal surface was added. In the present study, the prepared abutments were
scanned with a Cerec 3D camera and their areas were estimated with the Cerec 3 Volume
Program.
In this study, thermomechanical cyclic loading aged the specimens, and the stress for all
specimens was standardized and reproducible. In addition, this aging method
corresponds to 5 years in vivo.20 However, this assumption has not yet been systematically
verified with different materials and is only based on the extrapolation of 4-year-clinical wear
data on amalgam fillings and 6-months wear of composite resin inlays.20 This correlation was
only used for the wear rate tests. The clinical validity of the thermomechanical loading device for
tensile strength tests is yet to be determined.
In summary, the crowns made from polymeric blocks showed significantly lower tensile
strength than the glass ceramic crowns. In order to achieve adequate, long-term adhesion
clinically, the bonding to such blocks must be further optimized. Further studies should also test
other pretreatment methods for industrially polymerized resins such as silanization, silica
coating, or application of methacrylate monomers.
CONCLUSION
Within the limitations of this study, commercially polymerized resin CAD/CAM crowns
presented significantly lower tensile strength than that of glass ceramic crowns. On the other
hand, air abrasion increased the tensile strength of polymeric CAD/CAM crowns with the resin
cements tested, except for VAR. All specimens with resin CAD/CAM crowns failed adhesively
between the cements and the polymeric crowns.
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TABLES
Table I: Summary of products used.
Framework,
manufacturer
Cement,
manufacturer
Composition of the bonding agents and cements short name
Test groups
PMMA resin
artBloc Temp,
Merz Dental,
Lütjenburg,
Germany, Lot.No
14408
RelyX Unicem
(Lot.No 361930),
3M ESPE, Seefeld,
Germany
Powder: alkaline (basic) fillers, silanated fillers,
peroxy components, pigments, substituted
pyrimidine
Liquid: methacrylate monomers containing
phosphoric acid groups, acetate, initiators,
stabilizers
RXU
G-Cem (Lot.No
0801091), GC
Europe, Leuven,
Belgium
Powder: fluoro-alumino-silicate glass, initiator,
pigments
Liquid: 4-META, UDMA, dimethacrylate, water,
phosphoric ester monomer, initiator,
camphorquinone
GCM
artCem GI (Lot.No
7806520)
artCem ONE
(Lot.No 5811037)
Merz Dental,
Lütjenburg,
Germany
Powder: barium-aluminum-silicate glass, nano-
fluorapatite, pigments, initiator
Liquid: polyacid, methacrlylate , initiator
2-hydroxyethylmethacrylate, dimethacrylate,
initiator, stabilizers
ACG
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Variolink II
(Lot.No
K41833/K39878)
Syntac Classic
(Lot.No
J280035/J27820),
Bis-GMA, TEGDMA, UDMA, benzoylperoxide,
inorganic fillers, ytterbium trifluoride, Ba-Al
fluorosilicate glass, spheroid mixed oxide, initiator,
stabilizers, pigments
Primer: TEGDMA, maleic acid. dimethacrylate,
water
adhesive: PEGDMA, maleic acid, glutaraldehyde,
water
VAR
Control group
Glass ceramic
VITA Mark II,
VITA Zahnfabrik,
Bad Säckingen,
Germany, Lot.No
18090
Variolink II
(Lot.No
K41833/K39878)
Syntac Classic
(Lot.No
J280035/J27820),
Monobond S
(Lot.No J17658)
Heliobond (Lot.No
G09457) Ivoclar
Vivadent, Schaan,
Liechtenstein
Bis-GMA, TEGDMA, UDMA, benzoylperoxide,
inorganic fillers, ytterbium trifluoride, Ba-Al
fluorosilicate glass, spheroid mixed oxide, initiator,
stabilizers, pigments
Primer: TEGDMA, maleic acid. dimethacrylate,
water
adhesive: PEGDMA, maleic acid, glutaraldehyde,
water
ethanol, water, silane
Bis-GMA, dimethacrylate, initiators, stabilizers
CONT
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Table II: Tensile strength values (MPa) with 95% confidence intervals and significant
differences of all tested groups.
Groups Pretreatment Aging Mean (SD) 95%CI Failure types
RXU
No treatment Initial 0 (0) - all between
polymeric crown
and cement
Aging 0 (0) -
50 µm Al2O3 Initial 2.2 (0.15) (1.9,2.6)b
Aging 1.9 (0.20) (1.4,2.4)z
110 µm Al2O3 Initial 2.6 (0.28) (1.9,3.3)A
Aging 2.0 (0.33) (1.2,2.7)Y
GCM No treatment Initial 0 (0) -
Aging 0 (0) -
50 µm Al2O3 Initial 1.4 (0.22) (0.9,1.9)a
Aging 0.0 (0.0) -
110 µm Al2O3 Initial 2.8 (0.15) (2.5,3.2)A
Aging 1.0 (0.20) (0.5,1.5)X
ACG No treatment Initial 0 (0) -
Aging 0 (0) -
50 µm Al2O3 Initial 2.1 (0.13) (1.8,2.5)b
Aging 1.0 (0.19) (0.5,1.5)y
110 µm Al2O3 Initial 2.3 (0.15) (2.0,2.7)A
Aging 1.2 (0.13) (0.9,1.5)X,Y
VAR No treatment Initial 0 (0) -
Aging 0 (0) -
50 µm Al2O3 Initial 0 (0) -
19228-orig2-figs-edits 18
Aging 0 (0) -
110 µm Al2O3 Initial 0 (0) -
Aging 0 (0) -
CONT etched Initial 7.3 (2.2) (4.9;9.6) all in the glass
ceramic crown etched Aging 6.4 (0.9) (5.4;7.5)
* Different superscripts represent a significant difference in each row, a,b between the initial
groups sandblasted with 50 µm Al2O3 (P<.001); x,y,z between the aged groups sandblasted with
50 µm Al2O3 (P=.002); A between the initial groups sandblasted with 110 µm Al2O3 (P=.236) and
X,Y,Z between the aged groups sandblasted with 110 µm Al2O3 (P=.014)
19228-orig2-figs-edits 19
Table III: P-values of the 2 sample Student’s t-test with mean difference and 95% confidence
interval between initial and aging groups within 1 pretreatment and within each cement.
Group Pretreatment P-value Mean difference 95% CI
RXU No treatment - - -
50µm Al2O3 .231 0.31 (-0.22;0.83)
100µm Al2O3 .151 0.65 (-0.26;1.55)
GCM No treatment - - -
50 µm Al2O3 <.001 1.37 (0.89;1.85)
100 µm Al2O3 <.001 1.82 (1.31;2.34)
ACG No treatment - - -
50 µm Al2O3 <.001 1.16 (0.67;1.65)
100 µm Al2O3 <.001 1.15 (0.72;1.57)
VAR No treatment - - -
50 µm Al2O3 - - -
100 µm Al2O3 - - -
CONT etched .416 0.83 (-1.46;3.15)
19228-orig2-figs-edits 20
Table IV.: P-values of the 2 sample Student’s t-test with mean difference and 95% confidence
interval between with 50 µm Al2O3 and 100 µm Al2O3 airborne-particle- abraded groups, within
aging or initial groups, and within each cement.
Group Aging / No Aging P-value Mean difference 95% CI
RXU Initial .230 -0.39 (-1.06,0.27)
Aging .932 -0.03 (-0.84,0.77)
GCM Initial <.001 -1.44 (-1.99,-0.90)
Aging <.001 -0.99 (-1.42,-0.55)
ACG Initial .378 -0.18 (-0.61,0.24)
Aging .421 -0.19 (-0.69,0.30)
VAR Initial - - -
Aging - - -
19228-orig2-figs-edits 21
FIGURES
Fig. 1. Design of tensile bond strength measurement.
Fig. 2. Mean tensile strength results of all tested groups.
19228-orig2-figs-edits 22
Fig. 3. Failure types after tensile strength measurements: A, fracture of glass ceramic crown. B,
fracture in cement/ crown interface; note that all cement remained on abutment.
A B